TDA chips for tone control in preamplifiers. Powerful and high-quality homemade sound amplifier. Operation of a pre-amplifier with a tone block

This stereo preamplifier is built around the popular NE5532 op amp and several discrete elements. Pre-amplifier suitable for working with any signal source, such as an mp3 player or computer, and in addition to a final power amplifier, it will allow you to get good sound at home.

The preamplifier has a tone block that allows you to adjust the low and high frequencies, as well as adjust the volume using three paired rotary potentiometers. Placing the potentiometers on the edge of the board eliminates the need for wires connecting the potentiometers to the board, which in turn improves the amplifier's noise performance.

The preamplifier is powered from a bipolar power supply with voltage from +/-18 to +/-30 volts.

Operation of a pre-amplifier with a tone block

The circuit diagram of the preamplifier is shown in the figure below:

The amplifier consists of two identical channels. Let's study the operation of a preamplifier using one of them. The input signal is fed to GP1 and goes directly to a high pass filter consisting of capacitor C1 (1uF) and resistor R1 (100k) with a cutoff frequency of about 1.5Hz, this effectively cuts off the DC component and the lowest frequencies.

Next, the signal goes to the non-inverting amplifier U1 (NE5532) and resistors R3 (10k) and R7 (4.7 k), which provides a signal amplification of 1.5 times. A small capacitor C3 (10 pF) prevents excitation, while C5 (1 µF) separates the circuits on amplifiers U1 and U2 (NE5532).

The frequency regulator is built on the U2 amplifier, and the frequency control itself is built in a classical way. Elements that make changes to characteristics are in a negative loop feedback amplifier U2. When both controls are in the center position, resistance X1 (derived from elements: R9 (10k), C9 (33 nF), C7 (4.7 nF), and also: P1 (100k), P2 (100k), R11 (10k ) and R12 (3.3 k) - “in the middle position”) between the input signal and the inverting input of the amplifier U2 is equal to the resistance X2 (obtained from the elements: R15 (10 k), C11 (33 nF), C13 (4.7 nF) and in the middle also: P1, P2, R11 and R12 - “in the middle position”) between the output of amplifier U2 and the inverting input. The gain A is expressed by the following dependence:

It is equal to 1 for the entire operating frequency range of the amplifier.

P1 is responsible for adjusting the low frequencies. For high frequencies, capacitors C9 and C11 are short-circuited, so adjustment with the potentiometer has no effect at these frequencies. The potentiometer is responsible for adjusting the high frequencies, and due to the exclusion of capacitors C7 and C13, the adjustment has no effect on the low frequencies.

The signal from the output of the frequency regulator goes through resistor R17 (4.7 k) to the volume control potentiometer P3 (100k) and then to the next amplification circuit, namely U5 (NE5532). Elements R19 (15k) and R21 (33k) configure U5 to work as an inverting amplifier with a gain of about 2. From the output of U5, the signal through the filter R23 (100P), C21 (1 uF) and R25 (100k) goes to the output of the preamplifier GP3 .

The supply voltage for the operational amplifiers is obtained using regulators U3 (78L15) and U4 (79L15), and is filtered using capacitors C15–C16 and C17–C18. In addition, the power supply to each of the four op-amps is smoothed using capacitors C19-C20 and C23-C26 (100 nF).

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Radio designer NE5532, which can be ordered from China. It usually comes in an assembly kit, so if you order it, you will need to be able to understand microcircuits and handle a soldering iron.

What's included?

• Instructions (on Chinese). This is not scary, because on the seller’s website the same instructions are offered in English.
• PCB. It is double-sided and has metallized holes.
• Two-channel variable resistors - 4 pcs. The rated power is 50 kOhm. They are designed to adjust the overall volume, midrange, bass and treble.
• Resistors with a minimum error of 1 percent.
• NE5532 chips - 2 pcs. They are low power amplifiers. They are designed for left and right channels.
• Diode bridge.

Preparing for assembly

To power the device you will need bipolar power supply or midpoint nutrition. The device is designed to be powered directly from a transformer. For this purpose, there is a middle point and two AC voltage contacts.

Since we have bipolar power supply, it will require two stabilizers.

Pre-amplifier assembly

NE5532 preamp test

When connecting, do not forget that the board has bipolar power supply. Connecting music and testing the sound of three different frequencies left a pleasant impression.

Background:
While building a home audio system, I encountered difficulties. One of them is mine tube amplifier power when connected to a source “directly” gives a boring, compressed sound. Without “tops” and “bottoms”, just a protruding lower middle. Moreover, the film sound is good, but my music (black metal) plays poorly.

Obviously, loudness compensation is required. The purchase, in general, solved the problem, but the sound quality (in general) deteriorated. The preamp went to the mezzanine to gather dust.

I decided to use a tone block in my system instead of loudness compensation.
There are Chinese ones already assembled, for example, on two 6n1p and a kenotron:

But in Russia, from the website, I took this set - a tube tone block-preamplifier based on a 6n2p-ev double triode.

For 4000 rubles I received (all parts are new):

1100+1100 rubles - Two sets of parts for assembling two mono channels.
1000 rubles - TAN 15-01, toroidal power anode-heat transformer.
130 rubles - Power supply board.
270 rubles - Choke D15N (50mA, 10H).
400 rubles - shipping (from St. Petersburg to Novosibirsk).

Parcel contents:


Close-up of the power supply components:


A choke, and two double triodes 6n2p-ev - produced in 1972 and 1976 - which is strange. I thought they would be one year old. And these are structurally different even to the eye:


(P.S.: The author wrote that all his lamps are from 1976. My 1972 found its way into his collection in some unknown way, and he didn’t put it in my car on purpose. I suggested listening to this for now. Didn't offer free lamp replacement. He did not apologize for the missing radio components. In general, the seller does not use any polite words (“thank you,” “hello,” “goodbye”) in correspondence, probably for reasons of principle).

Preamp boards, two mono channels:


Set of parts No. 1:


Set of parts No. 2:


“Manuscript” (Xerox copy in A4) with handwritten marks that I could not fully decipher. Just evaluate the level of performance:


Almost soldered boards (differences from the original photo on the website are immediately visible - coupling capacitors and lamp sockets):


The amplifier was assembled on a breadboard (I apologize for the quality of the photos):




Sound quality:

Average.

But the tone block, it seemed to me, is not quite optimally designed for high-quality speaker systems. A little “narrow” or something.

Adjustment within: ±8dB.
LF: 300 Hz.
HF: 3 kHz.
band: 20-20000Hz. (±0.3dB).
THD: 0.05%.
out: 2V、maximum 20V or more.

Because of this, the adjustment occurs in a limited range, which is clearly audible.

I would like adjustment LF: 100 Hz And HF: 10 kHz, and maybe even wider.
The seller said that the scheme suits many people.

Suggested by low frequencies replace capacitors C3, instead of the original 15 nF, put 10 nF, like Manakov.

By high frequencies suggested capacitor C1 of 1 nF (according to Manakov’s scheme, Matyushin’s C2) should be changed downwards.

Advantages:

Quite inexpensive.

Easy assembly.

Flaws:

You need two mono channels for the stereo option, which increases the inconvenience of adjustment, and twice the number of “twists”.

The instructions could have been more accurate.

The most common variable resistors are used, with characteristic “B”, so the timbres are not adjusted smoothly, but sharply, abruptly.

Complete radio components in the kit are the cheapest.

The kit was missing 4 resistors. The radio tubes were not paired.

There is no assembly diagram, so I could not assemble it correctly until I myself found an error in the markings applied to the board.

It turned out to be the exit block at the rear. It has reverse polarity compared to other pads on the board:

In general, the scheme proposed by Matyushin is less successful than Manakov’s scheme.

Manakov’s circuit is much simpler, the gain is less (which is good), since Matyushin’s is redundant.

In addition, Matyushin’s circuit requires three expensive coupling capacitors per channel, instead of Manakov’s one.

P.S.
I decided to make a Manakov tone block from Matyushin’s tone block. According to the scheme, we remove the following elements:


We get this type of board:


The biggest influence on the sound quality of this preamplifier is the coupling capacitor and capacitor C2 in the tone block. I installed paper-oil K40U-2 (0.1 µF 350V) instead of film Wima, because I did not find anything more suitable. On C2 you need to put either high-voltage ceramic or mica. I installed SGM-1.

The sound quality has increased greatly compared to the original circuit, but the K40U-2 capacitor begins to sound good only after it has “warmed up” (at least half an hour). I don’t know what caused this, but it’s a fact.

P.P.S.
K40U-2 changed to polypropylene Taiwanese:


The sound has changed compared to the K40U-2 - on my black metal the “middle” has become more dynamic and harsh. But at the same time, the sound became less “singing” and “soulful” on rock ballads, etc.

P.P.P.S.
A 6N2P-EV lamp can be replaced with a 6N1P-EV lamp without changing the circuit - just pulled out one and inserted another (as you can see, I also bypassed the electrolytes in the anodes with 1uF 250V film capacitors, I didn’t hear a difference, but let them be):


The only difference I heard is that the 6N1P-EV plays a little quieter. Well, inside they are different in design:


P.P.P.P.S.
As a result of my barbaric, random experiments, one of the two 6N2P-EV lamps fell victim. Interestingly, the newer lamp, from 1976, burned out.

Stay tuned.